1. Field of Invention
The present invention relates to a light emitting diode, and more particularly to the light emitting diode package structure with a mixture of glue.
2. Description of Related Art
Light emitting diodes have high reaction speeds, smaller volumes, lower power consumption, less heat radiation and extended lifetimes and have therefore gradually replaced conventional incandescent or halogen lamps. Applications for light emitting diodes, like the indication light for electronic apparatus, the back light source of the liquid crystal display (LCD) and the illuminator, are continually being extended as technology progresses.
As LED illumination and efficiency increases, the packaging process faces two major challenges, heat dissipation and optical characteristic. Regarding heat dissipation, high power light emitting diode generates simultaneously lots of light beams and heat. The heat needs to be dissipated quickly and efficiently. Otherwise, the accumulated heat results in high temperature that diminishes the illumination and shortens the lifetime. In another aspect for optical characteristic, the light emitting diode typically uses epoxy resin to package the die. High temperature and ultraviolet irradiation affects the optical characteristics of the epoxy resin. Consequently, optical transparency is gradually decreased with the extended usage period and the refraction index is therefore lessened.
In conventional packaging process for LEDs, the auto-encapsulating step or molding step proceeds after the die bonding step and the wire-bonding step. General die bonding processes use silver paste or transparent insulating paste to mount the chip on the substrate such that the heat generated from the chip is conducted to the substrate or heat sink of the package through the silver paste or transparent insulating paste. However, the silver paste and transparent insulating paste cannot bear such voluminous heat conduction caused by the raised power and temperature of the light emitting diode device. In this way, the optical deterioration and heat deterioration result in light emitting diode device failure.
Moreover, the composed material of the light emitting diode and laser diode have a refraction index larger than 2.5, and the conventional gel or resin has a refraction less than 1.5. Therefore, the large difference between the chips and the composed material decreases the light emitting efficiency because of the lower total internal reflection angle of the emitted light from the chip after packaging.
In addition to primitive characteristics of mechanical strength and heat dissipation efficiency, the optical characteristic of the composed material should be considered in order to satisfy the current requirement for light emitting diode package structures.